1. Field of the Invention
The present invention is directed to a onecomponent adhesive and/or sealing mass which is stable and pumpable at temperatures up to 30.degree. C., to a process for preparing this mass, as well as to the use of this mass for bonding and/or sealing one or more materials of the same or different origin to a composite.
Polyurethane adhesives are known as one-part systems, hardenable with moisture or with heat, as two-part systems or as hot-melt adhesives (hot melts).
2. Description of the Prior Art
In the U.S. Pat. Nos. 3,933,725 and 3,707,521 there are described the preparation of hardenable polyurethanes by reacting diphenylmethanediisocyanate with polyoxypropylenediols and polyoxpropylenetriols in one-step or two-step processes.
The products obtained in this way may be processed to a moisture hardenable one-component adhesive mass either directly or, as described in the German Offenlegungsschrift No. 30 19 356, by the addition of latent hardeners, e.g. aldimines or oxazolidines. As described in the German Offenlegungsschriften Nos. 29 46 085, 25 42 500, 25 50 156 and 29 29 224 there are obtained in the heat hardenable one-part systems by reacting with blocking agents for isocyanate groups, e.g. phenols, caprolactames, ketoximes and malonic esters.
In case of two-component systems the above described masses are not hardened by means of moisture, but by means of mixing them with a second component, containing a hardener (e.g. diamine, diol or amino alcohol).
Such systems are described in the U.S. Pat. Nos. 3,228,914 and 3,114,734 as well as in the European Pat. No. 0 153 456.
One-part systems are very easily handable, because no mixing process is necessary before the application.
In case of two-part systems the two components must usually be present in an exact stoichiometric mixing ratio, and a good mixing must be guaranteed. The drawback of a moisture hardenable mass consists therein that a hardening takes place relative slowly from the outer layers to the inner layers, and thereby the part to be bonded must sometimes be fixed during a longer time. In the case of two-part adhesive masses the hardening takes place in the whole mass at the same time. A high stability immediately after the application, corresponding to one object of this invention, is also not obtained.
The blocked systems have the disadvantage that the bonded arrangement must be heated to a temperature from 80.degree. C. to 200.degree. C. in order to obtain a hardening of the adhesive mass. This heating step of the parts having sometimes large surfaces may not always be realized, especially in series production in the industry.
A further group of polyurethane adhesive masses are the hot-melt adhesives (hot melts).
They are composed of thermoplastic materials, which are heated for the processing to a temperature of 90.degree. C. to 200.degree. C. and are applied as liquid mass. During cooling the mass solidifies again and forms quickly a rigid bonding.
One differs between nonreactive and reactive hot-melt adhesives.
The nonreactive hot-melts have the disadvantage, due to their thermoplastic behavior, that their mechanical charactertistics are strongly dependent on the temperature. At an elevated temperature they soften again, and at lower temperatures they tend to a development of brittleness, and that is why they may only be used in a narrow temperature range.
The reactive hot-melts are characterized in that the mass contains free reactive isocyanate groups, which after the application allow together with moisture a cross-linkage, and whereby an elastic mass is produced, which is no longer meltable.
The preparation and the composition of such reactive hot-melt adhesives is described in DE-PS No. 24 01 320 and DE-OS No. 32 36 313.
These reactive hot-melt adhesives are during coating only limited non-sag, so that with coatings having a thickness of more than 2 mm the still hot mass flows away. Therefore, their use is limited to certain applications. For example, a bonding of a window in automotive vehicles is not practicable with these adhesives.
A further drawback is the melting of the mass prior to the application. The solid product, usually supplied in drums or cans containing 20 to 30 liters, must be, before it may be pumped and applied, heated from the top with a heatable plate and must directly be pumped through heatable hoses. The heating capacity of the plate, i.e. how much adhesive is molten during a time unit, determines the maximum amount of transport. Due to thermical decomposition the material may not be overheated. The maximum amounts of transport of good, optimally adjusted pumping plants amount to 800 g to 1000 g/min. from a drum (200 liters) and 400 to 500 g/min. from a can containing 20 to 30 liters.